Geology students report on last month's New Zealand earthquake

Posted by mjs76 at Mar 09, 2011 09:54 AM |
Stephen Angood and Alex Walker are two exchange students from our Department of Geology, currently studying for their third year at the University of Canterbury in Christchurch, NZ. Alex writes:
Geology students report on last month's New Zealand earthquake

Christchurch Cathedral after the quake (image: Wikipedia)

On 4 September 2010 at 4.35am, we experienced what later turned out to be a 7.1 magnitude earthquake; we were in our flat at the time.

At the start it sounds like a heavy lorry rapidly getting closer, with vibration building. Then the earthquake actually hit, and there was a large amount of lateral (sideways) movement for approximately 30 seconds. It was very loud at the time, with the whole building creaking and groaning around us, and a roaring/grinding noise in the ground beneath.

The shaking was more of a jerking motion rather than continual swaying, and the building literally felt like rubber around us. Books and items were falling off shelves, and it was incredibly difficult to stand up during the earthquake because balance is so hard to maintain!

Power was immediately lost throughout Christchurch, for days in some people's cases, while a much more limited area lost water supplies. But overall, for a magnitude 7.1, its effects were relatively minimal. There were no deaths, and limited destruction of property. There was no damage to our accommodation, although the university was closed for two weeks while buildings were checked.

For us this was actually quite a cool experience, especially as we study geology; to experience an earthquake of this magnitude isn't an opportunity many people get!

Aftershocks then went on for months afterwards, gradually decreasing in magnitude and frequency... until 22 February 2011. At 12.51pm, Christchurch was hit by a magnitude 6.3 aftershock, occurring due to the presence of uneven regional stress left by the September earthquake. It lasted for maybe 10 seconds, again with large lateral movement in roughly the same orientation.

quakemap.jpg
Location and intensity of the February 2011 Christchurch earthquake (image: USGS/Wikipedia)

I was in the flat at the time, and basically dived under the bed as soon as it started; it felt and sounded completely different to the smaller aftershocks we'd been feeling. Again items were falling from the shelves in my room and in the kitchen area.

Steve happened to be in the Geology Department at the time, trying to walk down a corridor to a lab session. In his words, "I was walking and then went into the wall," as the aftershock shook the building. Being on the second floor at the time, the shaking was magnified for him, compared to those on the ground.

The aftershocks immediately after the 6.3 were strong; standing outside, we could see actually buildings swaying, and glass flexing in windows. One of the blocks of flats took some minor damage, with pieces of concrete dislodged from the roof. With electricity knocked out for hours again, we didnt know how badly Christchurch's central business district had been hit until later on. Beyond this, we think what has been shown on the world news since speaks well enough for the consequences.

Since then, we've transferred to the University of Otago in Dunedin, where hopefully there will be a little less seismic activity for the rest of this semester!

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